Agent Based Modeling

What is ABM?• Easiest way to describe it is to demo building one

• Agent Based Modeling is a modeling technique

• Made up of autonomous decision making entities called agents

• A collection of interacting agents make up a system

• When we run the system we should see emergent properties. Things that happen because of the interactions between agents.

Simple agent rules, can result in different sorts of complex and interesting behavior in the system.

Lets build a simple ABM1. The Environment

Field

Grass

Mud

Creating a simple ecosystem

2. Agents

Agent. An agent is an autonomous, dynamic rule-based entity within a defined environment.

Predator Agents

Prey Agents

Creating a simple ecosystem

3. Create Rules

Environment Rules• Grass turns to mud if eaten• Grass grows back after certain amount of time

Predator Rules

• Will chase prey?• Need to eat prey for energy• Can reproduce• With no energy the agent will die

Prey Rules • Needs grass for energy• Can Reproduce if near other prey• Walk around• With no energy the agent will die

http://modelingcommons.org/browse/one_model/2401

Running the Model

Construct Virtual World

World develops through agent interaction

Virtual world events driven by agent interactions.(Emergent Behavior)

Creation Stages

Go Back and edit the Virtual World

Predator – Prey game

“This model simulates a predator-prey relationship. The

population consists of wolf packs (predators) and

sheep herds (prey), some controlled by students via

HubNet clients and some androids controlled by the

computer. The wolves gain energy from consuming

sheep, and the sheep gain energy from consuming

grass (a primary producer). The model allows students

to examine simple population dynamics like those

modeled through the Lotka-Volterra equations in a

participatory way.”

Models can be participatory

Other Models

• SKIN Model (Simulating Knowledge Dynamics in

Innovation Networks)o http://cress.soc.surrey.ac.uk/SKIN/

o Agents are firms, universities, consumers, suppliers

o Agents have to produce an initiative product to survive

• Supply chain modelingo http://www.sciencedirect.com/science/article/pii/S0925527308002016

o http://egon.cheme.cmu.edu/ewocp/docs/GonzaloEWO-GG-11Dec.pdf

• Consumer decision makingo http://ccl.northwestern.edu/netlogo/models/community/customerBehavi

or -based on customer questionnaires

Key Points to ABM• Captures Emergent Phenomena

As the components of a system interact with each

other, and influence each other through these

interactions, the system as a whole exhibits emergent

behavior (Roetzheim)

• Flexibility

Can easily be adapted to new constraints – new rules,

agents, changes to environment. Agile?

• Lots of ABM software available

Personal Opinion• ABM has is good at different things depending on

what you are trying to model:o Explanatory models

o Exploratory models

o Predictive purposes

ABM Platforms• Netlogo (very easy, designed to be like Logo)

• Repast Symphony ( Java , Eclipse based )

• Repast HPC ( C++ based for cluster/super

computer simulations )

Useful sites

• Netlogo: https://ccl.northwestern.edu/netlogo/

• Journal of Artificial Societies and Social Simulation:

http://jasss.soc.surrey.ac.uk/

• Modeling Commons http://modelingcommons.org/